It is important to sight in, or adjust, the mechanical or telescopic sight of a gun to be assured that the bullet goes to the exact point that the shooter was aiming at through the sights. Sighting in a gun is usually accomplished by mounting the gun to a fixed stand, aiming at a target, firing a shot, and then adjusting the sight of the gun depending on where the bullet hit the target. The process is repeated until the shooter is satisfied with the accuracy of the sight.
Bore sighting using a light source was developed so that a gun could be sighted in without expenditure of ammunition and without the need to go to an area that was safe enough to shoot in. In this method, a light is projected down the barrel of the gun. When the light is emitted, it hits a target placed a predetermined distance away. The center of the light beam is ascertained and the user then adjusts the gun sights accordingly.
One problem encountered using bore sighting systems is that the housing holding the light source does not always fit accurately inside the gun chamber to provide an accurate beam of light. Since every different caliber gun has a different size barrel, the user may only get an approximate fitting of housing to chamber, or the user may have to buy a different apparatus for each of their guns.
U.S. Pat. No. 5,454,168 to Langner is one bore sighting apparatus which uses a light source. In Langner, the light source is enclosed in a single, cylindrical stepped housing which is placed in the breech of the gun. The housing is stepped so that the single housing is able to fit a limited number of pre-determined different caliber guns. Another bore sighting apparatus is U.S. Pat. No. 4,481,561 to Lanning. In Lanning, the light and light power source are both enclosed inside a housing which is shaped like a standard cartridge.
The disadvantages facing a user of a bore sighting apparatus are that either they have to buy a separate unit for each caliber gun they desire to sight in, or they are only able to get an approximate fit to a limited number of different caliber guns. It is desirable to provide a single, inexpensive system for bore sighting in which the housing holding the light source can be accurately positioned in all the different caliber guns a user has.